Characterization of non-typhisalmonella isolated from children admitted to hospitals with bacteremia in Kilifi and Nairobi

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Non-typhi salmonellae (NTS) are well known worldwide as causes of food borne diseases, which are characterized by gastrointestinal illnesses. Infected individuals experience mild gastrointestinal illnesses which are self-limiting and antimicrobial treatment not recommended. But among the young children, the elderly and immunosuppressed individuals the illness can lead to disease complications such as bactaeremia and other serious invasive diseases. This problem may be compounded by multidrug resistance (MDR) among the non-typhi salmonella, with resistance to four or more of the commonly available antimicrobials often being encountered. Studies in Kenya have shown that MDR among the Salmonellae is a serious problem. As Salmonella spp. acquire more resistance, they become more difficult to treat, hence leading to even greater morbidity and mortality. It is therefore important to monitor the susceptibility profiles of the prevailing NTS to commonly available antimicrobial drugs. This study aimed to characterize NTS isolated from children less than 5 years of age admitted to the hospitals with bacteremia in Nairobi and Kilifi. Characterization was done by biochemical and serological typing of the NTS, antimicrobial susceptibility of the isolates, and through DNA analysis including; plasmid analysis of both resistant and sensitive NTS by gel electrophoresis and analysis by pulsed field gel electrophoresis (PFGE) of (Xba-1) and (Spe-1) digested genomic DNA fragments. A total of 2212 blood samples were obtained from children 0-5 years of age of which 1296 (58.1%) and 916 (41.4%) samples were from Nairobi and Kilifi respectively. The number of samples positive for NTS was 148 (6.7%) out of which 118 (79.7% were isolated from Nairobi and 30 (20.3%) from Kilifi. The main NTS serotypes identified were Salmonella enterica serotype Typhimirium 99 (66.9%), Salmonella enterica serotype Enteritidis 43 (29.1%) and other salmonella species 6(4.1%). In Nairobi 56% of Salmonella isolated were resistant to three or more drugs while in Kilifi less than 10% were resistant. Large plasmids of 98-100 kb pairs were found all ampicillin resistant and multidrug resistant Salmonella. The PFGE results of endonuclease digested DNA revealed that 70% cases had the same NTS serotypes as their contacts at home. In conclusion there were two main serotypes of Salmonella isolated from the children; Salmonella typhimurium and Salmonell enteritidis. Salmonella isolates from Nairobi were more resistant to ampicillin, cortrimoxazole, chloramphenicol and tetracycline than isolates from Kilifi. S. typhimurium was more resistant than other salmonellae PFGE though expensive is a useful tool for epidemiological studies particularly in cases of disease outbreaks. Because cases and controls had the same NTS infection; siblings and parents of the sick children may have been the sources of NTS infections. Therefore these asymptomatic carriers of NTS (as happens in typhoid) may play an important role in the epidemiology of NTS bacteremia in these children. More emphasis should be on disease prevention through public health measures and continuous antimicrobial susceptibility monitoring and surveillance.